Period Calculator
Free period calculator and menstrual cycle tracker. Predict next period, fertile window and ovulation day based on last period.
How to Use This Period Calculator
- 1Select the start date of your last period
- 2Enter your average cycle length (default is 28 days)
- 3Enter your typical period duration (default is 5 days)
- 4Click Calculate to see next period, ovulation and fertile window
Formula
Next Period = Last Period + Cycle Length. Ovulation = Last Period + (Cycle Length − 14). Fertile Window = Ovulation Day − 5 to Ovulation Day + 1.
Frequently Asked Questions
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About Period Calculator
This menstrual period calculator predicts your next period date, ovulation day and fertile window based on your last period start date and cycle length. Ideal for tracking your cycle, planning, or simply understanding your menstrual rhythm better.